You are probably right that they are overpriced, but I'm embarrassed to admit I have no idea what a tone curve is.
nothing to be embarrassed about. there's loads i don't know or have never heard of, some of which you might know.
here's a decent tutorial.
Photoshop curves tutorial by Christopher Crawford
it's easier to see the big picture in photoshop than lightroom because photoshop has the black to white scale on the bottom and side of the graph. lightroom just puts it at the bottom. basically the bottom scale is what was captured when you took the picture, the side scale is the tone you want the corresponding bottom tone to be. ie, if you take the pure black point in the bottom left and pull it straight up a little bit then whatever spot you end up will be the darkest tone in your image. that's the whole idea in it's most simple form. you can add points on the line and move them around to wherever.
once you start messing with the individual color channels (red, green and blue) just remember that the opposite of rgb (red, green, blue) is cmy (cyan, magenta, yellow), so if you add red you're reducing cyan or vice versa. same for green and magenta, and blue and yellow. so if you want to add yellow to a photo you need to go to the blue channel.
all of these options are available in lightroom too, but you have to change your point curve to custom to access the red, green and blue channels.
vsco has actually scanned film and analyzed it to see which tones were characteristic of that specific film. that's why it costs what it does. i never learned what most films looked like so i could care less if it's scientifically accurate and couldn't tell the difference anyway, hence my view of it being overpriced.. my buddy who is a bit older and grumpy and recently switched to digital because he couldn't get some films anymore loves vsco cause he only has lightroom and doesn't want to learn about tone curves, so it's more than worth it to him.
